In a projection display apparatus such as a liquid crystal projector, a display element such as a liquid crystal panel is irradiated with light emitted from a light source such as a mercury lamp, and an image formed on the display element is enlarged and projected onto a screen through a projection lens.
A configuration of an optical system in the apparatus includes an optical unit (hereinafter referred to as an optical engine) which irradiates a liquid crystal panel with light emitted from a light source to form an image and a projection optical system which enlarges and projects the image formed on the liquid crystal panel through a projection lens. An optical engine in a color image display apparatus is provided with three liquid crystal panels for the three primary colors (RGB) as display elements, a color separating system for separating the colors of irradiation light, and a color synthesizing system for synthesizing the colors of an image. The projection optical system is provided with a lens shift mechanism for moving the projection lens in a direction perpendicular to an optical axis in order to adjust an image display position on a screen.
Here, as a method for fixing the projection lens so as not to easily move, a technique in which a lock plate is moved in an optical axis direction to perform a locking operation is disclosed (see Patent Document 1).